This application relates to the manufacture of photographic products, and particularly to the manufacture of photographic products with forehardened gelatin layers.
Photographic products containing gelatin or other cross-linkable polymers are conventionally hardened at one or more stages of manufacture and use to provide mechanical stability, to prevent softening and sticking, to provide abrasion resistance, or to modify the diffusion transfer characteristics of the product during processing. Typical hardeners and their functions are discussed in "The Hardening Of Gelatin And Emulsions" by Burness and Pouradier, appearing as Section III of Chapter 2 in The Theory of the Photographic Process, Fourth Edition, edited by T. H. James and published in 1977 by McMillan Publishing Company, Inc. of New York, New York. Generally speaking, photographic hardeners are water soluble materials which are effective under prescribed conditions to cross-link gelatin or other cross-linkable polymers that may be included in various layers of a photographic structure such as, for example, those described in U.S. Pat. No. 3,586,503, issued on June 22, 1971 to Lloyd D. Taylor and assigned to the assignee of this application.
For some purposes, the selected hardener can be added to a photographic composition, such as a photosensitive emulsion containing gelatin and silver halide, prior to coating, as described, for example, in U.S. Pat. No. 3,762,927, issued on Oct. 2, 1973 to Howard C. Haas and assigned to the assignee of this application. However, particularly in the case of photograhic products comprising multiple thin layers of coated materials for use in the production of photographic images by diffusion transfer processes, it has been found desirable to avoid the coating of compositions containing gelatin, or other cross-linkable polymeric constituents, and a hardener. To do so may result in undesired increases in the viscosity of the coating composition, or to mechanical instability in the gelatin-containing layers during coating.
Where it is desired to delay hardening of a gelatin-containing layer in a photographic product until during or after an image forming processing operation, various expedients have been proposed. For example, in U.S. Pat. No. 2,962,377, issued on Nov. 29, 1960 to Edwin H. Land and assigned to the assignee of this application, a processing composition containing a hardener is described that diffuses into a gelatin-containing layer during processing to effect hardening. Another approach is to include a hardener in a gelatin layer which is activated by an alklaine processing fluid, so that the principal hardening effect occurs after the processing fluid has been applied to the product. Of course, neither of these techniques is of use where forehardening is desired.
In U.S. Pat. No. 3,427,158, issued to David P. Carlson and Jerome L. Reid on Feb. 11, 1969 and assigned to the assignee of this application, photographic products and processes are described in which a hardener is included in an interlayer composition that does not contain gelatin, but does contain a polymeric latex that is inert in contact with the hardener. This latex composition is coated between layers containing gelatin, and serves in the finished product as a timing layer to delay certain diffusion transfer processes during image processing so that they occur after other processes. However, it has been found that inclusion of a hardener in the latex layer, while practicable and having been successfully used, may cause difficulties during coating because of undesirable interaction between the hardener and the gelatin at the interface between the timing layer and any adjacent gelatin-containing layers. Another problem is that the introduction of a hardener into the latex layer imposes undesired restrictions on both the composition and the pH of the latex layer, generally resulting in the need to coat at a pH out of the range in which the latex is most stable. The object of this invention is to facilitate the forehardening of gelatin and other cross-linkable polymers, while reducing the constraints on the coating process and on the chemistries of the various photosensitive, dye developer, timing and/or other layers that may be included in a given photographic product.
Briefly, the above and other objects of the invention are attained by the construction of a novel photographic product comprising as base sheet upon which there is coated a plurality of layers including a first carrier layer next to the base, an isolation layer over the carrier layer, and then one or more superposed layers comprising at least one layer containing gelatin or other cross-linkable (tannable) polymeric material. This product is made by coating the first layer as an aqueous composition containing a hardener and free of any polymeric constituent, such as gelatin, that will react with the hardener during coating. This layer may, however, include potentially cross-linkable constituents at concentrations low enough to inhibit cross-linking during coating. The isolation layer may simply be water, although diffusable constituents of a desired diffusion transfer system may be included if compatible with the hardener. Gelatin or other cross-linkable polymeric constituents that might interact with the hardener are preferably not included in this layer.
The invention will best be understood in the light of the following detailed description, together with the accompanying drawings.